FIG. 8 shows a cross-sectional view of a prior art semiconductor light detector shown in such as Japanese Patent Laid Open Publication No. 61-141175. In FIG. 8, the reference numeral 1 designates an N type region, and this region is produced by an epitaxial growth on a high resistance N.sup.- region 2 which has resistivity of 10 .OMEGA.cm. The reference numeral 3 designates a P.sup.+ region, and a pn junction section 4 which becomes a light receiving surface is produced by producing this P.sup.+ region. The reference numeral 5 designates a polycrystalline semiconductor region provided so as to separate the respective pn junction sections 4. The reference numeral 6 designates a protection film, and the reference numeral 7 designates a rear surface electrode. Besides, an ohmic electrode which is to be provided on the P.sup.+ region 3 is not shown because it is well known.
Prior to describing the semiconductor light detector of the above described structure, the problems in a semiconductor light detector comprising a plurality of light receiving elements arranged in an array will be described.
FIG. 9 shows a cross-section of such a semiconductor light detector. In FIG. 9, the reference numeral 11 designates a P type semicondcutor substrate, the reference numeral 13 designates an N type impurities dopes layer, the reference numeral 14 designates a pn junction section constituting a light receiving element, the reference numeral 16 designates a protection film, the reference numeral 17 designates a rear surface electrode, the reference numeral 20 designates a carrier generated by an incident light, and reference numerals 21 and 22 designate the proceeding directions of the carrier 20.
Only the photons incident on and having energy levels longer than the band gap energies of either the P type semiconductor substrate 11 or the N type impurities doped layer 13 generate carriers. The generated carriers are drifted by the electric field in the depletion layer at the neighbourhood of the pn junction section 14, thereby being separated to produce a voltage difference. Then, there arises a problem of cross-talk that the light incident to a region between adjacent photo diodes causes mutual interferences between the elements. This cross-talk is caused by the generation of electron hole pairs at a deep portion of the P type semiconductor substrate 11 when light having a small absorption coefficient is incident. For example, the carriers 20 generated by the incident light proceed not only in the direction 21 but also in the direction 22 to reach the adjacent picture element. Such cross-talk makes the positional boundary at a position sensor less distinct, and makes unclear the distinctions between adjacent signal peaks in an analysis sensor.
Noticing these problems, in the prior art semiconductor light detector, a polycrystalline semiconductor region 5 is provided between the pn junction sections 4, that is, between adjacent picture elements, thereby separating the respective picture elements. Furthermore in order to get rid of cross-talk of carriers at deep portions, a high resistance N.sup.- region 2 having a high resistivity of 10 .OMEGA.cm is provided as shown in FIG. 8. The lifetime of carriers at said N.sup.- region 2 is quite short, and therefore they all disappear before they reach the N type region 1.
In the prior art semiconductor light detector constituted in such a manner, as apparent from FIG. 8 the structure is very complicated, and therefore the production process becomes a complicated one. Furthermore, the distance between consecutive picture elements is restricted because there is a separation region, and the size of the device inevitably increases. Furthermore, it is impossible to reduce the inter-picture element region which is insensitive to the incident light, and there arises a restriction in the function while operating as an analysis sensor.